The present invention relates to a differential provided in a final reduction device of a power transmission system for a motor vehicle or a central differential provided in a four-wheel drive motor vehicle.
In an automobile, a differential is provided between axles of drive wheels for permitting one of the drive wheels to turn at a different speed from the other wheel, while power of an engine is transmitted from a drive shaft to the drive wheel axles.
In brief, the differential comprises a differential case, encasing two differential pinion gears and two bevel side gears meshed with pinion gears, and internally splined to drive wheel axles, and a ring gear attached to the case and engaged with a drive pinion. The differential operation is performed in accordance with the speed difference of the drive wheels caused by the difference of coefficient of friction of a road, even if the motor vehicle is travelling straight ahead which causes one wheel to turn faster than the other.
In order to avoid such a defect, nonslip differentials are used in many automobiles, in which two sets of clutch plates are provided for locking the drive wheel axles to the case. However, the structure of such a differential is complicated.
Japanese Utility Model Application Laid-Open 61-123250 discloses a system for controlling a differential comprising a worm gear and a worm wheel for permitting the differential operation when a motor vehicle makes a turn. When the vehicle travels on a straight road, the differential is in inoperative state because of the irreversible function of the worm gear.
However, in such a system, since the worm gear is used, the structure of the differential is complicated so that the manufacturing cost increases. Further, since the worm gear device has a large sliding resistance, the transmission efficiency is reduced and wearing of the gears increases.